Phonological and semantic strategies in immediate serial recall

It has been suggested that certain theoretically important anomalous results in the area of verbal short-term memory could be attributable to differences in strategy. However there are relatively few studies that investigate strategy directly. We describe four experiments, each involving the immediate serial recall of word sequences under baseline control conditions, or preceded by instruction to use a phonological or semantic strategy. Two experiments varied phonological similarity at a presentation rate of one item every 1 or 2 seconds. Both the control and the phonologically instructed group showed clear effects of similarity at both presentation rates, whereas these were largely absent under semantic encoding conditions. Two further experiments manipulated word length at the same two rates. The phonologically instructed groups showed clear effects at both rates, the control group showed a clear effect at the rapid rate which diminished with the slower presentation, while the semantically instructed group showed a relatively weak effect at the rate of one item per second, and a significant reverse effect with slower presentation. The latter finding is interpreted in terms of fortuitous differences in inter-item rated associability between the two otherwise matched word pools, reinforcing our conclusion that the semantically instructed group were indeed encoding semantically. Implications for controlling strategy by instruction are discussed.     

Phonological and semantic strategies in immediate serial recall

It has been suggested that certain theoretically important anomalous results in the area of verbal short-term memory could be attributable to differences in strategy. However there are relatively few studies that investigate strategy directly. We describe four experiments, each involving the immediate serial recall of word sequences under baseline control conditions, or preceded by instruction to use a phonological or semantic strategy. Two experiments varied phonological similarity at a presentation rate of one item every 1 or 2 seconds. Both the control and the phonologically instructed group showed clear effects of similarity at both presentation rates, whereas these were largely absent under semantic encoding conditions. Two further experiments manipulated word length at the same two rates. The phonologically instructed groups showed clear effects at both rates, the control group showed a clear effect at the rapid rate which diminished with the slower presentation, while the semantically instructed group showed a relatively weak effect at the rate of one item per second, and a significant reverse effect with slower presentation. The latter finding is interpreted in terms of fortuitous differences in inter-item rated associability between the two otherwise matched word pools, reinforcing our conclusion that the semantically instructed group were indeed encoding semantically. Implications for controlling strategy by instruction are discussed.     

On the Brain Response to Syntactic Anomalies: Manipulations of Word Position and Word Class Reveal Individual Differences

In two experiments, event-related brain potentials (ERPs) were recorded from 13 scalp locations while subjects read sentences containing a syntactically or a semantically anomalous word. The position (sentence-embedded vs sentence-final) and word class (open vs closed) of the syntactic anomalies were manipulated. In both experiments, semantically anomalous words elicited an enhanced N400 component. Syntactically anomalous closed class words elicited a widely distributed late positive wave (P600) regardless of the word's position and a smaller negative-going effect that was largest over anterior sites when the anomaly occurred in sentence-final position. The response to syntactically anomalous open class words revealed striking qualitative individual differences: These words elicited a P600 response in the majority of subjects and an N400 response in others. The proportion of subjects exhibiting the N400 response was greater when the anomaly occurred in sentence-final position. These results are interpreted in the context of prior findings, and implications for the hypothesis that syntactic and semantic anomalies elicit distinct brain potentials are discussed.     

Contextual mood priming following left and right hemisphere damage

This research examined the influence of mood-congruent and mood-incongruent contexts on recognizing affective prosody after brain damage. Predictions stemmed from an associative network theory of learning and memory. Thirty-three male subjects, 11 each in right hemisphere damaged (RHD), left hemisphere damaged (LHD), and normal control groups judged moods from the prosody of semantically neutral phrases. In one task, the prosodic stimulus phrases were judged in isolation. In another task, the phrases were preceded by short paragraphs which were either congruent or incongruent in emotional tone with the prosodic stimuli. These paragraphs were designed to prime specific mood choices. As anticipated, LHD subjects' prosodic mood recognition was more accurate when given congruent rather than incongruent affective contexts. Congruent contexts facilitated, and incongruent contexts disrupted, their prosodic mood judgments to the same extent as normals. RHD subjects showed a partial context decrement. They were less accurate than normal or LHD subjects in the congruent condition, and were unaffected by incongruent contexts. When given congruent biasing paragraphs, however, RHD subjects did experience facilitation on a par with that found for the other groups, indicating spared sensitivity to certain contextual factors. The distinction between automatic and effortful processes is offered as a potential explanation for the RHD group's pattern of performance.     

WORKING MEMORY CAPACITY DISSOCIATES LEXICAL AND SENTENTIAL CONTEXT EFFECTS

Abstract— Semantically associated and unassociated word pairs were embedded in normal meaningful sentences and in sentences that were semantically anomalous throughout The influence of lexical context was isolated via comparison of responses to the second words of the associated and unassociated pairs. The influence of sentence-level context was isolated by comparing responses to the same words in the two sentence types Subjects of high, medium and low working memory capacity (as evaluated by the reading span test) showed modulations of event-related brain potentials in response so lexical context. In contrast, only the high- and medium-capacity groups were responsive to purely sentence-level semantic context. The results demonstrate that sentential context influences the processing of words in intermediate sentence positions at normal reading speeds but that the on-line utilization of this context is more demanding of working memory than single-word contexts.     

Making sense of sentences in schizophrenia: electrophysiological evidence for abnormal interactions between semantic and syntactic processing

Event-related potentials to critical verbs were measured as patients with schizophrenia and healthy controls read sentences word by word. Relative to their preceding context, critical verbs were (a) congruous, (b) incongruous and semantically unrelated to individual preceding words (pragmatic-semantic violations), (c) incongruous but semantically related to individual preceding words (animacy-semantic violations), or (d) syntactically anomalous. The N400 was modulated normally in patients, suggesting that semantic integration between individual words within sentences was normal in schizophrenia. The amplitude of the P600 to both syntactic and animacy-semantic violations was reduced in patients relative to controls. The authors suggest that, in schizophrenia, an abnormality in combining semantic and syntactic information online to build up propositional meaning leaves sentence processing to be primarily driven by semantic relationships between individual words.     

Sensitivity to local sentence context information in lexical ambiguity resolution: evidence from left- and right-hemisphere-damaged individuals

Using a cross-modal semantic priming paradigm, the present study investigated the ability of left-hemisphere-damaged (LHD) nonfluent aphasic, right-hemisphere-damaged (RHD) and non-brain-damaged (NBD) control subjects to use local sentence context information to resolve lexically ambiguous words. Critical sentences were manipulated such that they were either unbiased, or biased toward one of two meanings of sentence-final equibiased ambiguous words. Sentence primes were presented auditorily, followed after a short (0 ms) or long (750 ms) interstimulus interval (ISI) by the presentation of a first- or second-meaning related visual target, on which subjects made a lexical decision. At the short ISI, neither patient group appeared to be influenced by context, in sharp contrast to the performance of the NBD control subjects. LHD nonfluent aphasic subjects activated both meanings of ambiguous words regardless of context, whereas RHD subjects activated only the first meaning in unbiased and second-meaning biased contexts. At the long ISI, LHD nonfluent aphasic subjects failed to show evidence of activation of either meaning, while RHD individuals activated first meanings in unbiased contexts and contextually appropriate meanings in second-meaning biased contexts. These findings suggest that both left (LH) and right hemisphere (RH) damage lead to deficits in using local contextual information to complete the process of ambiguity resolution. LH damage seems to spare initial access to word meanings, but initially impairs the ability to use context and results in a faster than normal decay of lexical activation. RH damage appears to initially disrupt access to context, resulting in an over-reliance on frequency in the activation of ambiguous word meanings.     

Sentence context effects on lexically ambiguous words: Evidence for a postaccess inhibition process

Two experiments were conducted to investigate the process involved in selecting the contextually appropriate meaning of a homograph. Both experiments employed a grammaticality decision task. In Experiment 1, the primary (more frequent) and secondary (less frequent) meanings of homographs were used as the target items requiring a “yes” decision. The results indicated that the effect of relative frequency of these meanings of homographs was reduced when the target word was preceded either by a semantically congruous or anomalous sentence context relative to when it was preceded by the grammatical morpheme “the” or “to.” Experiment 2 indicated that “no” decisions were consistently slower for syntactically unambiguous, but semantically ambiguous words (e.g., ORGAN, FEET) than for syntactically and semantically unambiguous words (e.g., CENT, LEND), irrespective of the type of preceding context. The results, taken as a whole, are best interpreted within the postaccess inhibition model of sentence-context effects suggested by Forster (1981).     

Memory and encoding of spoken discourse following right hemisphere damage: evidence from the Auditory Moving Window (AMW) technique

We investigated the hypotheses that impaired discourse processing following right hemisphere damage is mediated by task difficulty and is associated with deficits in discourse encoding. Spoken discourse passages differing in contextual predictability were presented to right hemisphere-damaged (RHD) patients and to non-brain-damaged (NBD) controls for subsequent recall using the Auditory Moving Window paradigm. To manipulate processing difficulty, speech segments were of normal or accelerated speech rates. The recall results showed that RHD adults recalled less than NBD controls overall and failed to recall major idea units better than minor idea units for high predictability passages presented at accelerated speech rates. Both RHD patients and NBD controls failed to recall major idea units better than minor idea units for low predictability passages, regardless of speech rate. The encoding results showed that RHD adults were both slower overall and differentially slower than NBD controls when listening to accelerated passage segments. Taken together, the encoding and recall results are consistent with the view that extracting passage gist under difficult listening conditions is especially vulnerable for patients with right hemisphere strokes.     

Rapid extraction of gist from visual text and its influence on word recognition

Two experiments explored rapid extraction of gist from a visual text and its influence on word recognition. In both, a short text (sentence) containing a target word was presented for 200 ms and was followed by a target recognition task. Results showed that participants recognized contextually anomalous word targets less frequently than contextually consistent counterparts (Experiment 1). This context effect was obtained when sentences contained the same semantic content but with disrupted syntactic structure (Experiment 2). Results demonstrate that words in a briefly presented visual sentence are processed in parallel and that rapid extraction of sentence gist relies on a primitive representation of sentence context (termed protocontext) that is semantically activated by the simultaneous presentation of multiple words (i.e., a sentence) before syntactic processing.     

Word associations are formed incidentally during sentential semantic integration

Sentential context facilitates the incidental formation of word associations (e.g., Prior, A., & Bentin, S. (2003). Incidental formation of episodic associations: the importance of sentential context. Memory and Cognition, 31(2), 306-316). The present study explored the mechanism of this effect. In two experiments, unrelated word pairs were embedded in coherent or semantically anomalous sentences. Anomalous sentences included either a local or a global anomaly. During an incidental study phase, participants performed a sentence categorization task. The strength of the incidental associations formed between two nouns jointly appearing in a sentence was probed by gauging their influence on subsequent paired-associate learning and cued recall in Experiment 1, and by assessing their associative priming effect in a subsequent unexpected explicit recognition test for single words in Experiment 2. In both experiments, significant associative memory was found for noun pairs studied in coherent sentences but not for those appearing in anomalous sentences, regardless of anomaly type. In a sentence rating task, global anomalies yielded less plausible sentences than local anomalies, however both types of anomalies were equally detrimental to the sentence integration process. We suggest that sentence constituents are incidentally associated during sentence processing, particularly as a result of sentence integration and the consolidation of a mental model.     

Processing homonymy and polysemy: effects of sentential context and time-course following unilateral brain damage

The present study investigated the abilities of left-hemisphere-damaged (LHD) non-fluent aphasic, right-hemisphere-damaged (RHD), and normal control individuals to access, in sentential biasing contexts, the multiple meanings of three types of ambiguous words, namely homonyms (e.g., "punch"), metonymies (e.g., "rabbit"), and metaphors (e.g., "star"). Furthermore, the predictions of the "suppression deficit" and "coarse semantic coding" hypotheses, which have been proposed to account for RH language function/dysfunction, were tested. Using an auditory semantic priming paradigm, ambiguous words were incorporated in dominant- or subordinate-biasing sentence-primes followed after a short (100 ms) or long (1,000 ms) interstimulus interval (ISI) by dominant-meaning-related, subordinate-meaning-related or unrelated target words. For all three types of ambiguous words, both the effects of context and ISI were obvious in the performance of normal control subjects, who showed multiple meaning activation at the short ISI, but eventually, at the long ISI, contextually appropriate meaning selection. Largely similar performance was exhibited by the LHD non-fluent aphasic patients as well. In contrast, RHD patients showed limited effects of context, and no effects of the time-course of processing. In addition, although homonymous and metonymous words showed similar patterns of activation (i.e., both meanings were activated at both ISIs), RHD patients had difficulties activating the subordinate meanings of metaphors, suggesting a selective problem with figurative meanings. Although the present findings do not provide strong support for either the "coarse semantic coding" or the "suppression deficit" hypotheses, they are viewed as being more consistent with the latter, according to which RH damage leads to deficits suppressing alternative meanings of ambiguous words that become incompatible with the context.     

Discourse-based emotional consistency modulates early and middle components of event-related potentials

In this study, participants read stories describing emotional episodes with either a positive or negative valence (Experiment 1). Following each story, participants were exposed to short sentences referring to the protagonist, and the event-related potential (ERP) for each sentence's last word was recorded. Some sentences described the protagonist's emotion, either consistent or inconsistent with the story; others were neutral; and others involved a semantically anomalous word. Inconsistent emotions were found to elicit larger N100/P200 and N400 than consistent emotions. However, when participants were exposed to the same critical sentences in a control experiment (Experiment 2) in which the stories had been removed, emotional consistency effects disappeared in all ERP components, demonstrating that these effects were discourse-level phenomena. By contrast, the ordinary N400 effect for locally anomalous words in the sentence was obtained both with and without story context. In conclusion, reading stories describing events with emotional significance determines strong and very early anticipations of an emotional word.     

Do people with autistic spectrum disorder show normal selection for attention? Evidence from change blindness

People in the general population are typically very poor at detecting changes in pictures of complex scenes. The degree of this ‘change blindness’, however, varies with the content of the scene: when an object is semantically important or contextually inappropriate, people may be more effective at detecting changes. Two experiments investigated change blindness in people with autism, who are known from previous research to be efficient in detecting features yet poor at processing stimuli for meaning and context. The first experiment measured the effect of semantic information while the second investigated the role of context in directing attention. In each task, participants detected the dissimilarity between pairs of images. Both groups showed a main effect of image type in both experimental tasks, showing that their attention was directed to semantically meaningful and contextually inappropriate items. However, the autistic group also showed a greater difficulty detecting changes to semantically marginal items in the first experiment. Conclusions point to a normal selection of items for attention in people with autism spectrum disorders, although this may be combined with difficulty switching or disengaging attention.     

Hemispheric contributions to lexical ambiguity resolution in a discourse context: evidence from individuals with unilateral left and right hemisphere lesions

In the present study, a cross-modal semantic priming task was used to investigate the ability of left-hemisphere-damaged (LHD) nonfluent aphasic, right-hemisphere-damaged (RHD) and non-brain-damaged (NBD) control subjects to use a discourse context to resolve lexically ambiguous words. Subjects first heard four-sentence discourse passages ending in ambiguous words and after an inter-stimulus interval (ISI) of either 0 or 750 ms, made lexical decisions on first- or second-meaning related visual targets. NBD control subjects, at the 0 ms ISI, only activated contextually appropriate meanings, though significant effects, as a group, were only seen in second-meaning biased contexts. Surprisingly, at the 750 ms ISI, these subjects activated both appropriate and inappropriate meanings in first-meaning biased contexts. With respect to the LHD nonfluent aphasic patients, the majority activated first meanings regardless of context at the 0 ms ISI, though effects for the group were not significant. At the 750 ms ISI, these patients again activated first meanings regardless of context, with significant effects for the group only seen in first-meaning biased contexts. With regard to the RHD patients, the majority activated second meanings regardless of context at the 0 ms ISI and first meanings regardless of context at the 750 ms ISI, though, as a group, the effects were not significant. In light of our previous findings (Grindrod & Baum, 2003, submitted), the present data are interpreted as supporting the notion that damage to the left hemisphere disrupts either lexical access processes or the time course of lexical activation, whereas damage to the right hemisphere impairs the use of context and leads to activation of ambiguous word meanings based on meaning frequency.     

Temporal parameters as cues to phrasal boundaries: a comparison of processing by left- and right-hemisphere brain-damaged individuals

Two experiments were conducted to examine the ability of left- (LHD) and right-hemisphere-damaged (RHD) patients and normal controls to use temporal cues in rendering phrase grouping decisions. The phrase "pink and black and green" was manipulated to signal a boundary after "pink" or after "black" by altering pre-boundary word durations and pause durations at the boundary in a stepwise fashion. Stimuli were presented to listeners auditorily along with a card with three alternative groupings of colored squares from which to select the presented alternative. Results revealed that normal controls were able to use both temporal cues to identify the intended grouping. In contrast, LHD patients required longer than normal pause durations to consistently identify the intended grouping, suggesting a higher than normal threshold for perception of temporal prosodic cues. Surprisingly, the RHD patients exhibited great difficulty with the task, perhaps due to the limited acoustic cues available in the stimuli.     

Dual-coding, context-availability, and concreteness effects in sentence comprehension: an electrophysiological investigation.

Event-related potentials were recorded in 2 experiments while participants read sentences in a word-by-word congruency judgment task. Sentence final words were either congruent, semantically anomalous (Experiments 1 and 2), or neutral (Experiment 2) with respect to sentence context. Half of all final words referred to concrete and half to abstract concepts. A different scalp distribution of the N400 to concrete and abstract final words was found for anomalous and neutral, but not congruent sentences. Although the interaction of context and concreteness is consistent with the context-availability model, the differential scalp distribution of effects for concrete and abstract words, as well as larger context effects for concrete words, was interpreted as being more consistent with an extended dual-code account of semantic processing.     

Appreciation of indirect requests by left- and right-brain-damaged patients: the effects of verbal context and conventionality of wording

Unilaterally right (RHD)- and left (LHD)-hemisphere-damaged patients were tested on their ability to discern the correct, nonliteral interpretation of indirect requests (e.g., "Can you open the door?") embedded in short vignettes and presented without any pictorial support. Each stimulus vignette incorporated two verbal cues--context and conventionality of form--designed to influence interpretations of a critical utterance located at the end of each vignette. Contexts were biased to encourage either the direct, literal reading of critical utterances as a question, or the indirect meaning of the utterance as a request for action. The critical utterances themselves were either high in conventionality (e.g., "Can you ...?") which encouraged an indirect interpretation, or low in conventionality (e.g., "Is it possible for you to ...?") which encouraged a direct interpretation. Results indicated that RHD patients were significantly impaired, relative to controls, in their ability to make judgments based on contextual information. RHD patients performed comparably to the aphasic, LHD group in the use of both context and conventionality. These results replicate earlier findings of disrupted indirect request comprehension by RHD patients tested in pictorially supported paradigms.     

Rapid processing of the meaning of sentences

It has been shown (Fischler & Bloom, 1979) that sentence contexts facilitate a lexical decision task for words that are highly likely sentence completions and inhibit the decision for words that are semantically anomalous sentence completions. In the present experiment, the sentence contexts were presented 1 word at a time, at rates from 4 to 28 words/sec. The facilitation for words that were likely sentence completions was marginal at the slower rates and absent at higher rates. In contrast, the inhibitory effects of semantic anomaly were apparent at all presentation rates. Several analyses suggested that the sentence contexts were becoming ineffective at the very highest presentation rates, but the high rates at which the sentence contexts still affected word recognition were taken as evidence that semantic information accrues at an early stage of sentence processing. Implications for Posner and Snyder’s (1975) theory of attention and for models of reading were discussed.     

The role of syntactic context in word recognition

This study examines the role of syntactic information in word recognition. Subjects made a word-nonword decision regarding a target string that was preceded by a syntactically appropriate word, a semantically related word, or an unrelated word. In Experiment 1, with syntactic and semantic trials assigned to separate blocks, syntactically and semantically appropriate context significantly reduced lexical decision for subsequent target words, compared with unrelated contexts. In Experiment 2, the syntactically and semantically primed trials were either blocked separately or mixed within the same block. Significant syntactic and semantic effects were both observed in the blocked condition, but only the semantic effect was obtained in the mixed condition